Nano-size materials have recently become a major research source due to their unique optical and electrical properties and their potential use in electronics or photoelectronic engineering. The field of nanostructured material or nanostructure includes both of multi-dimensional nanostructures such as nanotubes and self-assemblies and technology development applying thereof. The nanostructures can be classified into inorganic nanostructures, organic nanostructures, polymer inorganic nanostructures, porous high surface area nanostructures and bio-related nanostructures depending on materials. The inorganic nanostructures are structures getting attention in relation to mainly semiconductors, and quantum structures, single electronic devices, next-generation memory devices and self-recording media researches are included therein. The organic nanostructure field includes fullerene, carbon nanotubes, carbon nanofibers, diamond thin film, organic EL and the like. The polymer inorganic nanostructures have two major fields: nanostructured polymers and ceramic particles of nanoparticle. The porous high surface area nanostructures include activated carbon fibers, zeolites and photocatalytic particles. The bio-related nanostructures include drug delivery systems, biomimetic devices, high sensitive nanosensor materials and the like.
In particular, carbon nanotubes have been subject to numerous studies for years due to their unique physical and electrical properties. The carbon nanotubes exhibit subconductor, conductor or semiconductor properties according to the chirality of the tube itself, carbon atoms are connected by strong covalent bonds, which makes tensile strength about 100 times larger than steel, the carbon nanotubes has excellent flexibility and elasticity as well as chemical stability. The carbon nanotubes are industrially important in the manufacture of composite materials due to their size and specific physical properties, and have high utilization in electronic materials, energy materials and other fields. For example, the carbon nanotubes can be applied to electrodes of electrochemical storage devices such as secondary batteries, fuel batteries or super capacitors, electromagnetic wave shielding materials, field emission displays, or gas sensors.
Because the nanostructured materials are provided in the form of powder of tens of micrometer in the actual process, they can cause harmfulness to the human body and malfunction of electrical products due to dusting in the process. In particular, in the case of carbon-based organic nanostructures, it is difficult to be dispersed due to large difference from polymers desired to mix in the apparent density.
In order to solve these problems, the nanostructured material may be compressed, and as a method for compressing carbon nanotubes, usually a method of palletization is provided due to increase of the density and easy of handling and transportation.
The carbon nanotube product, for example, a pellet-type carbon nanotube product is convenient to be used in various processing devices. In order to granulating or pelletizing carbon nanotubes, two different conventional methods, i.e., a method of wet-type pelletizing carbon nanotubes followed by drying thereof and a method of dry-type pelletizing, are used.
In general, the dry-type palletization uses a pelletization drum which comprises a horizontally positioned rotation tube, and the inside of the tube is referred to as a palletization chamber. Granulation of the carbon nanotube powder is performed by pre-condensing powder for industrial use and tumbling down thereof from the wall of a tube rotating in the pelletization drum for granulation. The powder is agglomerated by Van-der-Waals force and electrostatic force making the dry-type pelletization possible, and for the dry-type pelletization, usually pressure of several tons is applied. Thus, there is a problem that pellets may be rebroken during the manufacturing process.
The wet-type pelletizing process is performed mainly by a liquid bridge between carbon nanotubes and the capillary force. In the past, when mixing the carbon nanotubes by the wet-type pelletization, excessive solvents such as water or ethanol are added due to bad distribution of moisture and a binder, and the added solvents are generally hot-air dried, or heat-dried by using a rotary drum dryer or an agitated pan, or a conveyer. However, in the case of the method using a rotary drum or an agitated pan, there is a worry that the product may be damaged by a rotor, and in the case of the method using a conveyer, the spatial efficiency is deteriorated. In the case of the general hot-air drying, the drying efficiency is largely deteriorated.